WaterWater

Earth’s WaterEarth’s Water We live on a planet that is dominated by We live on a planet that is dominated by

water. More than 70 % of the Earth's water. More than 70 % of the Earth's surface is covered with this simple surface is covered with this simple molecule. Scientists estimate that the molecule. Scientists estimate that the hydrosphere contains about 1.36 billion contains about 1.36 billion cubic kilometers of this substance mostly in cubic kilometers of this substance mostly in the form of a liquid (water) that occupies the form of a liquid (water) that occupies topographic depressions on the Earth. The topographic depressions on the Earth. The second most common form of the water second most common form of the water molecule on our planet is molecule on our planet is ice. If all our . If all our planet's ice melted, planet's ice melted, sea-level would rise by would rise by about 70 meters.about 70 meters.

Why study water?Why study water?

There are many organisms in this world There are many organisms in this world that can exist without oxygen, but all that can exist without oxygen, but all living creatures need water in order to living creatures need water in order to survive. Human beings, for example survive. Human beings, for example are between sixty-five and seventy are between sixty-five and seventy percent water. Most of the plants that percent water. Most of the plants that we use for food are between eighty-we use for food are between eighty-five and ninety percent water by five and ninety percent water by weight. weight.

And…And…

Water is used for life support in a Water is used for life support in a variety of capacities ranging from variety of capacities ranging from habitats to reproduction to animal body habitats to reproduction to animal body functions (i.e. digest food, transport functions (i.e. digest food, transport wastes, lubricate body joints, regulate wastes, lubricate body joints, regulate temperature, and soften body tissues). temperature, and soften body tissues). It is clear that life as we know it could It is clear that life as we know it could not exist on Earth without its most not exist on Earth without its most abundant and remarkable substance - abundant and remarkable substance - water. water.

Water propertiesWater properties Unique properties based on its Unique properties based on its

structurestructure Oxygen is more electronegative than Oxygen is more electronegative than

hydrogenhydrogen Electrons spend more time with Electrons spend more time with

oxygen than with hydrogenoxygen than with hydrogen This unequal sharing causes the oxygen This unequal sharing causes the oxygen

to be slightly negative and the hydrogens to be slightly negative and the hydrogens to be slightly positive.to be slightly positive.

Polar covalent bond Polar covalent bond ie unequal sharingie unequal sharing

Polarity of WaterPolarity of Water Since opposite electrical Since opposite electrical

charges attract, water charges attract, water molecules tend to attract each molecules tend to attract each other, making water kind of other, making water kind of "sticky." As the right-side "sticky." As the right-side diagram shows, the side with diagram shows, the side with the hydrogen atoms (positive the hydrogen atoms (positive charge) attracts the oxygen charge) attracts the oxygen side (negative charge) of a side (negative charge) of a different water molecule. different water molecule.

This attraction forms This attraction forms hydrogen bondshydrogen bonds..

Water StructureWater Structure

Why is polarity important?Why is polarity important?

Polarity causes Polarity causes molecules to molecules to interact in unique interact in unique ways that influence ways that influence lifelife

Encourages Encourages formation of formation of hydrogen bondshydrogen bonds

Water is “sticky”Water is “sticky”

Water is attracted to other water. This is Water is attracted to other water. This is called called cohesioncohesion. Water can also be . Water can also be attracted to other materials. This is called attracted to other materials. This is called adhesionadhesion. .

CohesionCohesion

Surface TensionSurface Tension

The walls of alveoli The walls of alveoli are coated with a thin film of are coated with a thin film of water & this creates a potential problem. Water water & this creates a potential problem. Water molecules, including those on the alveolar walls, are molecules, including those on the alveolar walls, are more attracted to each other than to air, and this more attracted to each other than to air, and this attraction creates a force called surface tension. This attraction creates a force called surface tension. This surface tension increases as water molecules come surface tension increases as water molecules come closer together, which is what happens when we closer together, which is what happens when we exhale & our alveoli become smaller (like air leaving exhale & our alveoli become smaller (like air leaving a balloon). Potentially, surface tension could cause a balloon). Potentially, surface tension could cause alveoli to collapse and, in addition, would make it alveoli to collapse and, in addition, would make it more difficult to 're-expand' the alveoli (when you more difficult to 're-expand' the alveoli (when you inhaled). Both of these would represent serious inhaled). Both of these would represent serious problems: if alveoli collapsed they'd contain no air & problems: if alveoli collapsed they'd contain no air & no oxygen to diffuse into the blood &, if 're-no oxygen to diffuse into the blood &, if 're-expansion' was more difficult, inhalation would be expansion' was more difficult, inhalation would be very, very difficult if not impossible. Fortunately, our very, very difficult if not impossible. Fortunately, our alveoli do not collapse & inhalation is relatively easy alveoli do not collapse & inhalation is relatively easy because the lungs produce a substance called because the lungs produce a substance called surfactant that reduces surface tension. surfactant that reduces surface tension.

SurfactantsSurfactants

Lung cells that produce surfactant

Adhesion & Capillary Adhesion & Capillary ActionAction

This phenomenon causes This phenomenon causes water to stick to the sides water to stick to the sides of vertical structures of vertical structures despite gravity's despite gravity's downward pull. downward pull.

Water's high surface Water's high surface tension allows for the tension allows for the formation of water formation of water droplets and waves, allows droplets and waves, allows plants to move water (and plants to move water (and dissolved nutrients) from dissolved nutrients) from their roots to their leaves, their roots to their leaves, and the movement of and the movement of blood through tiny vessels blood through tiny vessels in the bodies of some in the bodies of some animals. animals.

Capillary ActionCapillary Action

Surface tension is related to the cohesive properties Surface tension is related to the cohesive properties of water. of water. Capillary actionCapillary action however, is related to the however, is related to the adhesive properties of water. You can see capillary adhesive properties of water. You can see capillary action 'in action' by placing a straw into a glass of action 'in action' by placing a straw into a glass of water. The water 'climbs' up the straw. What is water. The water 'climbs' up the straw. What is happening is that the water molecules are attracted happening is that the water molecules are attracted to the straw molecules. When one water molecule to the straw molecules. When one water molecule moves closer to a the straw molecules the other moves closer to a the straw molecules the other water molecules (which are cohesively attracted to water molecules (which are cohesively attracted to that water molecule) also move up into the straw. that water molecule) also move up into the straw. Capillary action is limited by gravity and the size of Capillary action is limited by gravity and the size of the straw. The thinner the straw or tube the higher the straw. The thinner the straw or tube the higher up capillary action will pull the water up capillary action will pull the water

Water movement in plantsWater movement in plants

Plants take Plants take advantage of advantage of capillary action to pull capillary action to pull water from the water from the ground into ground into themselves. From the themselves. From the roots water is drawn roots water is drawn through the plant by through the plant by another force, another force, transpirationtranspiration. .

Water Transport in Water Transport in PlantsPlants

TerminologyTerminology

Heat= amount of energy associated Heat= amount of energy associated with the movement of atoms and with the movement of atoms and molecules in mattermolecules in matter

Temperature= measures the Temperature= measures the intensity of heatintensity of heat

Calorie= amount of energy needed Calorie= amount of energy needed to raise 1000g of water 1 degree C to raise 1000g of water 1 degree C

Specific Heat of WaterSpecific Heat of Water Water has a high Water has a high specific heat. Specific heat is . Specific heat is

the amount of energy required to change the the amount of energy required to change the temperature of a substance. Because water temperature of a substance. Because water has a high specific heat, it can absorb large has a high specific heat, it can absorb large amounts of heat energy before it begins to get amounts of heat energy before it begins to get hot. It also means that water releases heat hot. It also means that water releases heat energy slowly when situations cause it to cool. energy slowly when situations cause it to cool. Water's high specific heat allows for the Water's high specific heat allows for the moderation of the Earth's climate and helps moderation of the Earth's climate and helps organisms regulate their body temperature organisms regulate their body temperature more effectively.more effectively.

Water's high Water's high specific heat specific heat allows for the allows for the moderation of the moderation of the Earth's climate Earth's climate and helps and helps organisms organisms regulate their regulate their body body temperature temperature more effectively.more effectively.

An Example…An Example…

One way to observe this characteristic is to One way to observe this characteristic is to heat an empty pan over a fire. The pan heat an empty pan over a fire. The pan quickly becomes red hot and may start to quickly becomes red hot and may start to bum. Place the same pan over the fire with bum. Place the same pan over the fire with water in it and the liquid will absorb some of water in it and the liquid will absorb some of the heat. The pan will again become hot but the heat. The pan will again become hot but not as hot as before. The temperature of not as hot as before. The temperature of the water, even if it boils, will rise only a the water, even if it boils, will rise only a small amount compared to the temperature small amount compared to the temperature of the pan. of the pan.

Try It!Try It!A simple experiment!A simple experiment!

Simple ExperimentSimple Experiment A Pyrex measuring cup was filled with either water, rubbing A Pyrex measuring cup was filled with either water, rubbing

alcohol, or air, and then heated in a pan of simmering water.alcohol, or air, and then heated in a pan of simmering water. In the case of the air, a plastic covering was fashioned for In the case of the air, a plastic covering was fashioned for

the measuring cup in order to keep the volume of air in the the measuring cup in order to keep the volume of air in the cup contained.cup contained.

Initially, the cup and its contents were at room temperature. Initially, the cup and its contents were at room temperature. The temperature of the simmering water in the pan was The temperature of the simmering water in the pan was approximately 200 degrees Fahrenheit.approximately 200 degrees Fahrenheit.

A thermometer was placed in the measuring cup in order to A thermometer was placed in the measuring cup in order to measure the temperature of the contents of the cup. measure the temperature of the contents of the cup.

Temperature readings were taken every minute for ten Temperature readings were taken every minute for ten minutes. minutes.

The cup was then removed from the water and placed in a The cup was then removed from the water and placed in a cold water bath where the temperature of the cup's contents cold water bath where the temperature of the cup's contents was again measured every minute for ten minutes. was again measured every minute for ten minutes.

Time Water Alcohol Air

0 min 75 deg. F 75 deg. F 80 deg F

1 min 80 deg. F 83 deg. F 100 deg. F

2 min 84 deg. F 93 deg. F 118 deg. F

3 min 88 deg. F 106 deg. F 138 deg. F

4 min 94 deg. F 116 deg. F 158 deg. F

5 min 100 deg. F 126 deg. F 175 deg. F

6 min 106 deg. F 135 deg. F 185 deg. F

7 min 112 deg. F 143 deg. F 190 deg. F

8 min 119 deg. F 150 deg. F 192 deg. F

9 min 124 deg. F 155 deg. F 193 deg. F

10 min 129 deg. F 158 deg. F 193 deg. F

Data for Specific Heat Data for Specific Heat ActivityActivity

Graphs of the temp. Graphs of the temp. changeschanges

Heating vs. CoolingHeating vs. Cooling

A water molecule takes a large amount of A water molecule takes a large amount of energy with it when it evaporatesenergy with it when it evaporates

This leads to evaporative cooling This leads to evaporative cooling

Figure 2.12

Physical properties of Physical properties of waterwater

DensityDensity Density increases as temp decreasesDensity increases as temp decreases Water max density 4 degrees CWater max density 4 degrees C Molecules move apartMolecules move apart

Solvent propertiesSolvent properties Protects ions from one anotherProtects ions from one another Charged substances dissolveCharged substances dissolve Universal solventUniversal solvent

States of WaterStates of Water

States of WaterStates of Water

Like no other common substance, Like no other common substance, water exists in nature in all three water exists in nature in all three physical states:physical states:

Figure 2.10B

as a solidas a solid as a liquidas a liquid as a gas as a gas

Don’t forget the water Don’t forget the water cycle!cycle!

It is this quality which allows for the It is this quality which allows for the water cycle, the process whereby the water cycle, the process whereby the Earth's water is moved by the energy Earth's water is moved by the energy of the sun and the force of gravity of the sun and the force of gravity through a cycle of evaporation, through a cycle of evaporation, condensation, precipitation and condensation, precipitation and accumulation. accumulation.

Water is less dense as a Water is less dense as a solid.solid.

Most liquids Most liquids contractcontract (get smaller) when they (get smaller) when they get colder. Water is different. Water get colder. Water is different. Water contracts until it reaches 4contracts until it reaches 4°°C then it expands C then it expands until it is solid. Solid water is less until it is solid. Solid water is less densedense that that liquid water because of this. liquid water because of this. IfIf water worked water worked like other liquids, then there would be no like other liquids, then there would be no such thing as an ice berg, the ice in your soft such thing as an ice berg, the ice in your soft drink would sink to the bottom of the glass, drink would sink to the bottom of the glass, and ponds would freeze from the bottom up and ponds would freeze from the bottom up (not good if you are a fish)!(not good if you are a fish)!

DensityDensity

Water is less dense as a solid than as a liquid

When water freezes, it forms crystal structure which is spacious –leading to increase in volume

Thus ice floats in water

This insulates the This insulates the life underneath!life underneath!

More CharacteristicsMore Characteristics

Pure water has a neutral pH of 7, Pure water has a neutral pH of 7, which is neither acidic nor basic.which is neither acidic nor basic.

Pure water is a very poor conductor Pure water is a very poor conductor of electricity! If that is the of electricity! If that is the case, why do we have to case, why do we have to be so careful with our be so careful with our electrical appliances? electrical appliances?

Universal SolventUniversal Solvent Water is called the Water is called the

"universal solvent" "universal solvent" because it dissolves because it dissolves more substances than more substances than any other liquid. This any other liquid. This means that wherever means that wherever water goes, either water goes, either through the ground or through the ground or through our bodies, it through our bodies, it takes along valuable takes along valuable chemicals, minerals, and chemicals, minerals, and nutrients. nutrients.

Even Proteins! Even Proteins! Water soluble proteinWater soluble protein